An endmill is a generally cylindrical cutting tool which has a plurality of cutting edges around its outer periphery. The endmill usually includes a cylindrical shank which fits into an axial bore of a tool holder. Various designs have been suggested for securing the endmill in the tool holder against axial movement and against rotation of the endmill with respect to the holder.
One method of securing the endmill within the holder is to use a set screw threadably engaged in the wall of the holder which can be tightened against a flat formed on the shank of the endmill. The use of a radial set screw, however, has some disadvantages. Most significantly, the radial set screw tends to push the endmill off center within the holder thereby effecting the accuracy of the endmill.
Another method which has been used is to employ a collet and chuck. A tapered collet having an axial bore for receiving the tool is pressed into a tapered bore in the tool holder by a lock nut. The collet is compressed into engagement with the tool. In theory, the collet collapses uniformally around its circumference so that the tool is accurately positioned at the center of the holder. A non-pullout wedge may be used in conjunction with the collet to prevent axial and rotational movement of the endmill. A collet arrangement of this type is disclosed in the patent to Staron, U.S. Pat. No. 4,341,006.
While widely used, the standard collet chuck has several drawbacks. First, the interfacing surfaces of the collet and chuck body must be accurately machined which increases the cost of producing the holder. Further, the cumulative tolerances between parts limit the degree of accuracy which can be obtained.